Apple changing MAIL user default settings

In the last month or so, I started having Mail performing differently than it had been performing. first was to find the message filter (under View) was reset to filter the inbox, the second was to change the default composing mail to "automatically select best account". It took me a few days, wondering where my opened emails went when in "All inboxes", and why I'm sending emails from an account I don't want to send from.

My question for the community (apple expert hopefully)... what is the logic for having the choice "Automatically select best account" when composing a new email?